Radio and other high frequency telegraph transmitters



Dec. 26, 1939. D. F GEORGE 2,184,332

RADIO AND OTHER HIGH FREQUENCY TELEGRAPH TRANSMITTERS Filed April 30, 1937 7 L 6 T 5; i9 5 5 4 1 z i 0mm 0mm sol/Mi 35 I8 MVEFNEPGY sou/2:5

INVENTOR a. 650/265 BY f ATTORNEY Patented Dec. 26, 1939 UNITED STATES RADIO AND OTHER. HIGH FREQUENCY TELEGRAPH TRANSMITTERS Douglas Frank George, London, England, assignor to Radio Corporation of America, a corporation of Delaware Application April 30, 1937, Serial No. 139,865 In Great Britain May 12, 1936 4 Claims.

This invention relates to radio and other high frequency telegraph transmitters and more particularly to telegraph transmitters of the kind wherein keying is effected by varying in dependonce upon the position of a key or relay (hereinafter termed simply a key) the potential upon a screen grid of a tetrode or other high frequency tube of the screen grid type.

It is well known that if a tetrode or other screen grid tube be employed in a high frequency circuit, it is possible to utilize for keying purposes the change in tube impedance which occurs if the screen grid potential be changed from a normal value to a value approximating tocathode potential; in other words, it is known to effect keying of a high frequency tetrode or other high frequency tube having a screen grid by means of a key which varies the potential upon the screen grid. One important defect, however, of simple known keying arrangements of this kind is that comparatively heavy changes of high tension feed current with corresponding fluctuations of supply voltage and dangerous keying transients are caused by the keying, for the total current load taken from the high tension sup-ply varies sharply and to a considerable extent when the key or relay is moved from onev position to another.

The principal object of the present invention is to provide improved keying circuits of the kind referred to which shall be very simple and which, nevertheless, shall not present the defect above mentioned, i. e., which shall be such that the load upon the high tension supply source remains substantially constant irrespective of Whether the key contacts are open or closed.

According to this invention a keying circuit arrangement of the kind referred to comprises a tetrode or other high frequency tube of the screen grid type having its screen grid connected to a point upon a potentiometer resistance included between the positive terminal of the high tension supply source for the tube and the cathode point thereof and the key contacts are connected between the cathode point and a point between the screen grid and said positive terminal said last mentioned point being so chosen that the sum total feed current taken from the high tension supply source remains the same, or nearly the same, whether the key contacts be open or closed.

The invention is illustrated in the accompanying drawing which shows diagrammatically one embodiment thereof.

Referring to the drawing, l is a high frequency tetrode whose cathode point 2 (shown as constituted by the usual intermediate tap on a resistance 3 shunting the cathode 4) is grounded and Whose anode 5 is connected, as in the usual Way, through a choke 6 to the positive terminal 1 of a source (not shown) of high tension supply '5 whose negative terminal 8 is grounded. The control grid circuit and the output anode circuit of the screen grid tube are as well known per so.

As shown, the control grid 9 is connected to the cathode point 2 through a resistance ID, the high 10 frequency drive being applied through condenser ll, while the output coilv I2 is connected to the anode 5 through a condenser l3. The screen grid 14 of the tube is connected to the positive terminal 1 through a resistance I5, and 5 is also connected to the cathode point 2 through a second resistance 16 which latter is preferably shunted by a by-pass condenser 11. The key l8 or its equivalent (e. g.,,re1ay contacts) is connected between the cathode point 2 and a tapping 20 I9 upon the resistance I5 and the said tapping I9 is so chosen that whether the key be open or closed the total-feed current taken is substantially the same. In other words the said tapping point 19 is so chosen that the current which passes through the key contacts when closedi. e., when the tube is biassed to cut off-4s the same or nearly the same as the sum total of the anode current and screen grid current flowing when the key contacts are open.

In order that the invention may be'the better understood two practical numerical examples for a circuit arrangement as illustrated and above described will be set forth. For the first of these examples the high tension supply source 35 between terminals 1, 8, was 2,000 volts; the resistance value (hereinafter termed R1) between the positive terminal 1 and the tapping point I!) was 19,000 ohms; the resistance (hereinafter termed R2) between the tapping point 40 I9 and the screen grid 14 was 31,000 ohms; and the resistance (hereinafter termed R3) between the screen grid 14 and the cathode point 2 was 50,000 ohms. The screen grid tube was of the type now commercially known under the trade 45 designation Marconi D. E. S. 1. With these values the anode feed was ma. and the screen grid feed was 30 ma. with the key open, the total screen grid resistance to ground being 50,000 ohms and the total feed current being 50 75+30=105 ma. I Upon closing the key, the anode and the screen grid feed currents fell to zero the keying resistance being now 19,000 ohms and the total feed (through the key) being still ma. In the second example a screen grid tube of the 55 type commercially known under the trade designation Marconi D. E. S. 3 was employed with a high tension supply at terminals I, 8 of 500 volts. In this case R1 was 5,500 ohms; R2 was 7,000 ohms; and R3 was 12,500 ohms. With the key open the anode feed was ma. and the screen grid feed was 30 ma. making a total feed of ma., the screen grid resistance being 12,500 ohms. Upon closing the key, the anode and screen grid feed currents fell to zero but the total feed (through the key) remained at 90 ma. with a keying resistance of 5,500 ohms. Thus, in both these numerical examples the total feed or load upon the high tension supply source was practically the same irrespective of the position of the key and as movements of the key from mark to space may, in practice, be regarded as substantially instantaneous, there are practically no voltage or current surges and the high tension supply source remains steady.

Preferably the tapping point I9 is adjustable so that an accurate state of balance can easily be obtained by trial and error.

Though not limited to its application thereto the invention is, by reason of its simplicity and effectiveness, very advantageously applicable to small radio transmitters for use on aircraft and to other portable transmitters where the attainment of load stability, simplicity and light Weight are of major importance.

I claim:

1. In a telegraphy system, an electron discharge tube having an emission electrode and a plurality of auxiliary electrodes, means for causing wave energy to flow between said electrodes, and for interrupting the flow of the same and for utilizing a substantially constant amount of energy during said operations including a source of direct current potential connected at its positive terminal to one of said auxiliary electrodes and at its negative terminal to said emission electrode, a resistance in shunt to said source of direct current potential, a connection between a point on said resistance and another of said auxiliary electrodes, and a key movable between closed and open positions shunting a portion of said resistance the resistance of said potentiometer being distributed between said connections in such a manner that said auxiliary electrodes and resistance impose a substantially constant load on said source of direct current in all positions of said key.

2. In a telegraph system, an electron discharge tube having an emission element and a plurality of auxiliary electrodes, means for causing wave energy to flow between said electrodes, and means for interrupting the flow of the wave energy and for utilizing a substantially constant amount of energy during said operations, including a source of direct current potential having a positive point thereon connected to one of said auxiliary electrodes and a negative point thereon connected to said emission electrode, a resistance connected between said points, a connection between another of said auxiliary electrodes and a point on said resistance, and a key movable between closed and open positions shunting a portion of said resistance, the value of said resistance distributed between said connections being such that said auxiliary electrodes and resistance impose a substantially constant load on said source of':

DOUGLAS FRANK GEORGE. 

